Characterizing the mechanism and rate of calcium phosphate precipitation in aerobic granular sludge

Aerobic granular sludge (AGS) is a promising technology that has demonstrated the ability to recover phosphorus through the precipitation of calcium phosphate minerals within granules^1-3. However, more work is needed to better understand how to control and enhance mineral precipitation within the polymeric matrix of the granule as well as how the pre-existing mineral phases within the granule influence recovery. We performed calcium phosphate precipitation experiments using AGS in order to quantify the impact of calcium pre-enrichment and mineral presence on the extent and rate of phosphate removal. Results have indicated that calcium pre-enrichment and mineral accumulation increases the transition from amorphous calcium phosphate to more crystalline forms and increases the rate and magnitude of phosphorus removal. This work identifies conditions under which AGS enhances mineral phosphate precipitation and suggests that calcium treated granular sludge can be used to recover phosphorus as a stable calcium phosphate mineral.